PURPOSE:To obtain an integrated circuit which is improved for the reliability at the operating time by using a substrate structure ready in its manufacture by forming the substrate for associating an N-channel MOSFET by altering the surface of an N type silicon substrate to P type. CONSTITUTION:An N type silicon layer 2 is formed on one surface of an N type silicon substrate 1, and a P type region 3 is then formed on the surface of the silicon layer 2. The region 3 is formed by inverting the conductive type over part or the entire surface of the layer 2. The layer 2 is formed by epitaxial growing, and the region 3 is formed by introducing P type impurity to the surface layer by thermal diffusing. The N type impurity is introduced into the region 3 to form source and drain region, and a gate insulating film and a gate electrode are then, formed, thereby forming a D-RAM made of N-MOSFET.